Abstract: Experiment conditions for the isonicotinic acid-pyrazolone colorimetric method including the preservation time of water samples, chloramine T content, water bath time and the bath temperature were studied in this paper for optimal chromogenic reaction for the detection of the volatile cyanide in seawater.The results show that the sealed water samples with the cyanide concentration from 0.5 μg/L to 5 μg/L could be preserved up to 24 h at pH of 12. During the time course of 24 h to 30 h, the loss rate of volatile cyanide is inversely proportional to its concentration fitted with the quadratic equation.The optimum content of the chloramine T is 2 mg when the cyanide concentrations is less than 4 μg in water sample, and there is a positive linear correlation between the absorbance decrement and the increment of the chloramine T content beyond the optimum content.When the cyanide concentration is lower than 4 μg in water samples, the water bath time for full chromogenic reaction is within 20 minutes and the bath temperature is around 40℃.